1. Technical Field
The present disclosure relates to a display device with an adjustable viewing angle and a method for driving the display device with an adjustable viewing angle.
2. Description of Related Art
Generally, a display device usually has a wide viewing angle for the purpose of allowing the image to be seen for a plurality of viewers. However, at some times or in some places, for example, when reading confidential information or inputting a password, the effect of the wide viewing angle easily causes the confidential information to be peeped by other people, which causes the divulgation of the confidential information. Therefore, in order to meet two different demands, both providing the image for a plurality of viewers and treating the confidential information in public places, the display device with an adjustable viewing angle, that is switchable between a wide viewing angle display mode and a narrow viewing angle display mode, gradually becomes one of mainstream products on the display device market.
A conventional anti-peep mechanism of a display device may be substantially classified into several techniques as below:
I. Direct Installation of an Anti-Peep Sheet on an External Surface of the Display Device:
A typical anti-peep sheet prevents the viewers in side view from clearly reading the displayed information by inhibiting the brightness at a large viewing angle, so as to achieve the privacy protection. Although this method is easy and the material of the anti-peep sheet is common, the additional installation of one optical film affects the original on-axis optical property and display quality of to the display device. Moreover, whether to prevent peep is manually switched, resulting in much inconvenience in use of a user.
II. Control of a Backlight Source
A backlight source that emits light with high collimation is utilized. The backlight source is equipped with a voltage-controlled diffusion sheet, for example a polymer-dispersed liquid crystal (PDLC) film. When the voltage applied to the diffusion sheet is turned off, the voltage-controlled diffusion sheet diffuses the collimated light and a portion of light is directed towards the side view, so that a wide viewing angle mode is realized. When the voltage applied to the diffusion sheet is turned on, the voltage-controlled diffusion sheet does not cause diffusion of the original collimated radiation, so that a narrow viewing angle mode is achieved. In this method, the brightness for the side view is adjusted by controlling the scattering angle of the backlight such that the people positioned at the side view cannot read the displayed information. Although ideally other people can be completely prevented from peeping at the information, and the switching between the wide viewing angle mode and the narrow viewing angle mode is convenient, completely collimated light, however, cannot be achieved in an actual application due to difficulties in controlling the light path. Even though the light distribution at a large viewing angle can be decreased, but the brightness towards the large viewing angle cannot be decreased to a level of unavailable identification. Therefore, a desirable anti-peep effect cannot be obtained.
III. Additional Arrangement of a Viewing Angle Control Module Unit
A viewing angle control module (panel) is additionally disposed on a conventionally operated display module (panel). The wide viewing angle mode to and the narrow viewing angle mode are switched by applying a voltage to the viewing angle control module. In this method, there is no interference or damage to the originally displayed image under the wide viewing angle mode, so that the quality of the original image can be kept. While in the narrow viewing angle mode, the brightness for the side view can be significantly inhibited, such that the viewers viewing from the side cannot easily judge and read the displayed message. However, due to the constitution of two modules, the overall weight and thickness are increased by one fold, and relatively increase the manufacturing costs.
In view of the above, conventional anti-peep techniques of display devices achieve anti-peep effects, but simultaneously sacrifice some of original characteristics of display devices, such as display quality, optical property, thickness and weight. Therefore, the conventional anti-peep technique still has space for improvement.